This invention relates to oil pressure senders, and more particularly to an improved, transducer-type sender which utilizes a fluid pressure-responsive diaphragm in combination with a friction free variable resistor for producing an electrical signal that is proportionate to pressure changes in a fluid. Even more particularly this invention relates to a pressure sender of the type described which utilizes a novel, friction free, variable resistor device in the form of a conical compression spring, which overlies and is engagable against a spirally shaped resistor element.
It has long been commonplace to employ in automotive vehicles, for example, transducer-type fluid pressure indicators for monitoring the oil pressure in the engine crankcase. The sender is an electro-mechanical type of transducer, which utilizes a piston, diaphragm or similar member for transmitting variations in a fluid pressure to an adjustable resistor element, or the like, in an electrical indicator circuit. Typically the adjustable resistor element comprises a slidable or rotatable operating arm, which is moved in response to changes in the position of the mechanically operated member that is interposed between the elements and the fluid pressure system.
Regardless of the mechanical means employed for operating the adjustable resistor element, a major problem heretofore encountered with pressure senders of the type described has been the undesirable wear and tear which results from the repeated movement of the adjustable element in response to changes in fluid pressure. A primary reason for this wear is that most such variable resistors heretofore have employed a spring-loaded wiper contact which has sliding, frictional engagement with a resistance wire, such as for example a wire coil. Either the wiper or the coil is shifted axially one relative to the other selectively to introduce more or less of the resistance wire coil into an associated circuit. Regardless of the exact shape of the resistance wire element, and regardless also of whether the wiper or the coil itself is shifted one relative to the other, the result is the introduction of a substantial and undesirable amount of friction wear between their respective sliding surfaces. In the case of oil pressure senders of the type described, this friction wear tends to reduce undesirably the operating life of the sender.
It is a primary object of this invention, therefore, to develop an oil pressure sender of the type described which eleminates the above-noted undesirable frictional sliding movement between the components of its adjustable resistor.
To this end it is an object of this invention to employ in a pressure sender of the type described a novel resistor in the form of a conically shaped spring element, which is compressible axially relative to a stationary, spirally shaped resistor element in response to pressure changes in a fluid system that is being monitored, thereby to add to or remove resistance from an associated indicator circuit simply by introducing more or less of the conical spring wiper into engagement with the spiral resistor, and without introducing any sliding engagement whatsoever between the conical spring element and spiral resistor element.
Heretofore efforts have been made to utilize non-sliding contacts in variable resistors employed for indicating pressure changes in a system. In U.S. Pat. No. 2,439,092, for example, the resistance wire itself is secured in spiral form on a flexible diaphragm, which is interposed between a fluid pressure source and a segmental-spherical contact. As pressure increases the contact is forced against the wire and diaphragm, causing the latter to bow, so that as more and more of the surface of the contact is forced into engagement with the spiral resistance wire, the resistance in the circuit is diminished. The disadvantage of this type of mechanism, however, is that the resistance wire is secured on the flexible diaphragm and is therefore subjected to constant flexing, which tends to minimize the life of the resistor. Moreover, any flexing of the resistance wire itself results in a change in the resistance of the wire, thereby making it extremely difficult to calibrate when used in a sender of the type described herein.
U.S. Pat. No. 1,989,673 also discloses the use of a spirally wound resistance wire for regulating the amount of power delivered to a brake mechanism. Again, the disadvantage of such a system is that the resistance wire itself is wound in spiral form and is flexed axially during use, thereby minimizing the overall life of the mechanism and also making it extremely difficult to calibrate. Similar concepts are disclosed in U.S. Pat. Nos. 488,121, 260,622, and 266,911.
British Pat. No. 265,676 discloses a variable resistor in the form of a convolutely wound wire spring, the smaller end of which is driven by a screw toward and away from a plane surface which has been metallized by the application thereto of, for example, suitable conducting material in the form of Indian Ink. As the coils are pressed toward the conductive ink surface the resistance is reduced, and conversely, as the coil is shifted away from the conductive surface the resistance in the circuit is increased. Again, it is the convolute spring itself which is functioning as the resistance wire.
It is a further object of this invention, therefore, to provide an improved oil pressured sender which utilizes a flat, spirally shaped resistance material of the type described which is stationary during use, so that the life of the sender is prolonged, and so that its calibration is simplified, as compared to prior such devices.
Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims, particularly when read in conjunction with the accompanying drawings.